Additive Composition for Transmission Oil Containing Hydrated Alkali Metal Borate and Hexagonal Boron Nitride

ABSTRACT

Disclosed are additive compositions for transmission oils comprising an oil dispersion of a hydrated alkali metal borate and an oil dispersion of hexagonal boron nitride, as well as lubricating oil compositions containing the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/999,712, filed Dec. 4, 2007, which is further a continuation of U.S.application Ser. No. 10/624,240, filed Jul. 22, 2003. The foregoingrelated applications, in their entirety, are incorporated herein byreference.

FIELD OF THE INVENTION

This invention is directed to an additive composition for a transmissionoil. More particularly, this invention is directed to an additivecomposition comprising an oil dispersion of a hydrated alkali metalborate and an oil dispersion of hexagonal boron nitride, as well aslubricating oil compositions containing the same.

REFERENCES

The following references are cited in this application as superscriptnumbers:

-   ¹Peeler, U.S. Pat. No. 3,313,727, Alkali Metal Borate E.P.    Lubricants, issued Apr. 11, 1967-   ²Adams, U.S. Pat. No. 3,912,643, Lubricant Containing Neutralized    Alkali Metal Borates, issued Oct. 14, 1975-   ³Sims, U.S. Pat. No. 3,819,521, Lubricant Containing Dispersed    Borate and a Polyol, issued Jun. 25, 1974-   ⁴Adams, U.S. Pat. No. 3,853,772, Lubricant Containing Alkali Metal    Borate Dispersed with a Mixture of Dispersants, issued Dec. 10, 1974-   ⁵Adams, U.S. Pat. No. 3,997,454, Lubricant Containing Potassium    Borate, issued Dec. 14, 1976-   ⁶Adams, U.S. Pat. No. 4,089,790, Synergistic Combinations of    Hydrated Potassium Borate, Antiwear Agents, and Organic Sulfide    Antioxidants, issued May 16, 1978-   ⁷Adams, U.S. Pat. No. 4,163,729, Synergistic Combinations of    Hydrated Potassium Borate, Antiwear Agents, and Organic Sulfide    Antioxidants, issued Aug. 7, 1979-   ⁸Frost, U.S. Pat. No. 4,263,155, Lubricant Composition Containing an    Alkali Metal Borate and Stabilizing Oil-Soluble Acid, issued Apr.    21, 1981-   ⁹Frost, U.S. Pat. No. 4,401,580, Lubricant Composition Containing an    Alkali Metal Borate and an Ester-Polyol Compound, issued Aug. 30,    1983-   ¹⁰Frost, U.S. Pat. No. 4,472,288, Lubricant Composition Containing    an Alkali Metal Borate and an Oil-Soluble Amine Salt of a Phosphorus    Compound, issued Sep. 18, 1984-   ¹¹Clark, U.S. Pat. No. 4,534,873, Automotive Friction Reducing    Composition, issued Aug. 13, 1985-   ¹²Brewster, U.S. Pat. No. 3,489,619, Heat Transfer and Quench Oil,    issued Jan. 13, 1970.-   ¹³Salentine, U.S. Pat. No. 4,717,490, Synergistic Combination of    Alkali Metal Borates, Sulfur Compounds, Phosphites and Neutralized    Phosphate, issued Jan. 5, 1988

All of the above patents are herein incorporated by reference in theirentirety to the same extent as if each individual patent wasspecifically and individually indicated to be incorporated by referencein its entirety.

STATE OF THE ART

High load conditions often occur in gear sets such as those used inautomobile transmissions and differentials, pneumatic tools, gascompressors, centrifuges, high-pressure hydraulic systems, metal workingand similar devices, as well as in many types of bearings. When employedin such environments, it is conventional to add an extreme-pressure(E.P.) agent to the lubricant composition and, in this regard, alkalimetal borates are well known extreme-pressure agents for suchcompositions.^(1-11, 13) E.P. agents are added to lubricants to preventdestructive metal-to-metal contact in the lubrication of movingsurfaces. While under normal conditions termed “hydrodynamic”, a film oflubricant is maintained between the relatively moving surfaces governedby lubricant parameters, and principally viscosity. However, when loadis increased, clearance between the surfaces is reduced, or when speedsof moving surfaces are such that the film of oil cannot be maintained,the condition of “boundary lubrication” is reached; governed largely bythe parameters of the contacting surfaces. At still more severeconditions, significant destructive contact manifests itself in variousforms such as wear and metal fatigue as measured by ridging and pitting.It is the role of E.P. additives to prevent this from happening. For themost part, E.P. agents have been oil soluble or easily dispersed as astable dispersion in the oil, and largely have been organic compoundschemically reacted to contain sulfur, halogen (principally chlorine),phosphorous, carboxyl, or carboxylate salt groups which react with themetal surface under boundary lubrication conditions. Stable dispersionsof hydrated alkali metal borates have also been found to be effective asE.P. agents.

Moreover, because hydrated alkali metal borates are insoluble inlubricant oil media, it is necessary to incorporate the borate as adispersion in the oil and homogenous dispersions are particularlydesirable. The degree of formation of a homogenous dispersion can becorrelated to the turbidity of the oil after addition of the hydratedalkali metal borate, with higher turbidity correlating to lesshomogenous dispersions. In order to facilitate formation of such ahomogenous dispersion, it is conventional to include a dispersant insuch compositions. Examples of dispersants include lipophilicsurface-active agents such as alkenyl succinimides or other nitrogencontaining dispersants as well as alkenyl succinates.^(1-4, 12) It isalso conventional to employ the alkali metal borate at particle sizes ofless than 1 micron in order to facilitate the formation of thehomogenous dispersion.¹¹

In addition, anti-sticking agents are often employed in automotive gearboxes to provide smooth synchronization and good shiftability. Examplesof such anti-sticking agents include phosphates, phosphites,phosphionates, thiophosphates, carbamates, molybdenum dithiocarbamatesand dithiophosphates.

It is also known that boron nitride exhibits friction modifyingproperties in lubricants. For example, U.S. Pat. No. 4,787,993, issuedNov. 29, 1988 to Nagahiro, discloses a lubricant effective for thereduction of friction which comprises dispersing a finely powderedaromatic or polyamide resin into a fluid fat or oil, which mayadditionally contain molybdenum disulfide, organic molybdenum or boronnitride.

Furthermore, U.S. Pat. No. 4,715,972, issued Dec. 29, 1987 to Pacholke,discloses a solid lubricant additive for gear oils comprising solidlubricant particles combined with a stabilizing agent and a fluidcarrier, wherein the solid lubricant particles are selected from thegroup consisting of molybdenum disulfide, graphite, cerium fluoride,zinc oxide, tungsten disulfide, mica, boron nitrate, boron nitride,borax, silver sulfate, cadmium iodide, lead iodide, barium fluoride, tinsulfide, fluorinated carbon, PTFE, intercalated graphite, zincphosphide, zinc phosphate, and mixtures thereof. This patent furtherdiscloses that such lubricant additive provides the gear oil withimproved demulsibility, stability and compatibility characteristics ofthe gear oil when contaminated with water.

Accordingly, it is an object of the present invention to provide alubricant additive composition having good anti-sticking properties whenused in transmission oils.

SUMMARY OF THE INVENTION

The present invention provides a novel additive composition for atransmission oil comprising:

(a) an oil dispersion of a hydrated alkali metal borate; and

(b) an oil dispersion of hexagonal boron nitride;

wherein the weight ratio of the hydrated alkali metal borate to thehexagonal boron nitride is in the range of about 95:5 to about 5:95.

The additive composition of the present invention may be suitablyemployed in both manual transmission gear oils and automatictransmission oils. Preferably, the additive composition will be employedin a manual transmission gear oil.

The present invention further provides a lubricating oil compositioncomprising a major amount of a transmission oil of lubricating viscosityand an effective synchronizer sticking reducing amount of the additivecomposition described above. Preferably, the transmission oil is amanual transmission gear oil.

Among other factors, the present invention is based in part upon thesurprising discovery that the unique combination of an oil dispersion ofa hydrated alkali metal borate and an oil dispersion of hexagonal boronnitride provides a significant and unexpected reduction in synchronizersticking when used as an additive composition in a manual transmissiongear oil.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the present invention is directed to a novel additivecomposition for a transmission oil comprising (a) an oil dispersion of ahydrated alkali metal borate, and (b) an oil dispersion of hexagonalboron nitride, wherein the weight ratio of the hydrated alkali metalborate to the hexagonal boron nitride is in the range of about 95:5 toabout 5:95.

Typically, the oil dispersion of hydrated alkali metal borate willcontain a hydrated alkali metal borate, a dispersant, optionally adetergent, and an oil of lubricating viscosity.

Preferably, the dispersant employed in the oil dispersion of hydratedalkali metal borate will be selected from the group consisting of apolyalkylene succinimide, a polyalkylene succinic anhydride, apolyalkylene succinic acid, a mono- or di-salt of a polyalkylenesuccinic acid, and mixtures thereof. Optionally, the oil dispersion ofhydrated alkali metal borate will also contain a detergent, such as ametal sulfonate, preferably an alkylaromatic calcium sulfonate or otherGroup II metal sulfonate that acts in the present compositions to helpprovide for a homogeneous dispersion.

The oil dispersion of hydrated alkali metal borate preferably includesthose compositions comprising from about 10 to 75 weight percent of thehydrated alkali metal borate; from about 2 to 40 weight percent of adispersant; and from about 30 to 70 weight percent of an oil oflubricating viscosity, all based on the total weight of the oildispersion.

Each of the components in the additive composition of the presentinvention will be described in further detail below.

Hydrated Alkali Metal Borate

Hydrated alkali metal borates are well known in the art. Representativepatents disclosing suitable borates and methods of manufacture include:U.S. Pat. Nos. 3,313,727; 3,819,521; 3,853,772; 3,912,643; 3,997,454;and 4,089,790.¹⁻⁶

The hydrated alkali metal borates suitable for use in the presentinvention can be represented by the following general formula:

M₂O.xB₂O₃ .yH₂O

wherein M is an alkali metal, preferably sodium or potassium; x is anumber from 2.5 to 4.5 (both whole and fractional); and y is a numberfrom 1.0 to 4.8. More preferred are the hydrated potassium borates,particularly the hydrated potassium triborates. The hydrated borateparticles will generally have a mean particle size of less than 1micron.

In the alkali metal borates employed in this invention, the ratio ofboron to alkali metal will preferably range from about 2.5:1 to about4.5:1.

Oil dispersions of hydrated alkali metal borates are generally preparedby forming, in deionized water, a solution of alkali metal hydroxide andboric acid, optionally in the presence of a small amount of thecorresponding alkali metal carbonate. The solution is then added to alubricant composition comprising an oil of lubricating viscosity, adispersant and any optional additives to be included therein (e.g., adetergent, or other optional additives) to form an emulsion that is thendehydrated).

Because of their retention of hydroxyl groups on the borate complex,these complexes are referred to as “hydrated alkali metal borates” andcompositions containing oil/water emulsions of these hydrated alkalimetal borates are referred to as “oil dispersions of hydrated alkalimetal borates”.

Preferred oil dispersions of alkali metal borates will have a boron toalkali metal ratio of about 2.5:1 to about 4.5:1. In another preferredembodiment, the hydrated alkali metal borate particles generally willhave a mean particle size of less than 1 micron. In this regard, it hasbeen found that the hydrated alkali metal borates employed in thisinvention preferably will have a particle size where 90% or greater ofthe particles are less than 0.6 microns.

In the oil dispersion of hydrated alkali metal borate, the hydratedalkali metal borate will generally comprise about 10 to 75 weightpercent, preferably 25 to 50 weight percent, more preferably about 30 to40 weight percent of the total weight of the oil dispersion of thehydrated borate. Unless otherwise stated, all percentages are in weightpercent.

The additive compositions and lubricant compositions of this inventioncan further employ surfactants, detergents, other dispersants and otherconditions as described below and known to those skilled in the art.Optionally, the additive compositions contain an alkylaromatic orpolyisobutenyl sulfonate.

The oil dispersions of hydrated alkali metal borates employed in thisinvention generally comprise a dispersant, an oil of lubricatingviscosity, and optionally a detergent, that are further detailed below.

Dispersant

The dispersant employed in the oil dispersion of hydrated alkali metalborate used in this invention can be ashless dispersants such as analkenyl succinimide, an alkenyl succinic anhydride, an alkenyl succinateester, and the like, or mixtures of such dispersants.

Ashless dispersants are broadly divided into several groups. One suchgroup is directed to copolymers which contain a carboxylate ester withone or more additional polar function, including amine, amide, imine,imide, hydroxyl, carboxyl, and the like. These products can be preparedby copolymerization of long chain alkyl acrylates or methacrylates withmonomers of the above function. Such groups include alkylmethacrylate-vinyl pyrrolidinone copolymers, alkylmethacrylate-dialkylaminoethy methacrylate copolymers and the like.Additionally, high molecular weight amides and polyamides or esters andpolyesters such as tetraethylene pentamine, polyvinyl polysterarates andother polystearamides may be employed. Preferred dispersants areN-substituted long chain alkenyl succinimides.

Alkenyl succinimides are usually derived from the reaction of alkenylsuccinic acid or anhydride and alkylene polyamines. These compounds aregenerally considered to have the formula

wherein R¹ is a substantially hydrocarbon radical having a molecularweight from about 400 to 3000, that is, R¹ is a hydrocarbyl radical,preferably an alkenyl radical, containing about 30 to about 200 carbonatoms; Alk is an alkylene radical of 2 to 10, preferably 2 to 6, carbonatoms, R², R³, and R⁴ are selected from a C₁-C₄ alkyl or alkoxy orhydrogen, preferably hydrogen, and x is an integer from 0 to 10,preferably 0 to 3. The actual reaction product of alkylene succinic acidor anhydride and alkylene polyamine will comprise the mixture ofcompounds including succinamic acids and succinimides. However, it iscustomary to designate this reaction product as a succinimide of thedescribed formula, since this will be a principal component of themixture. See, for example, U.S. Pat. Nos. 3,202,678; 3,024,237; and3,172,892.

These N-substituted alkenyl succinimides can be prepared by reactingmaleic anhydride with an olefinic hydrocarbon followed by reacting theresulting alkenyl succinic anhydride with the alkylene polyamine. The R¹radical of the above formula, that is, the alkenyl radical, ispreferably derived from a polymer prepared from an olefin monomercontaining from 2 to 5 carbon atoms. Thus, the alkenyl radical isobtained by polymerizing an olefin containing from 2 to 5 carbon atomsto form a hydrocarbon having a molecular weight ranging from about 400to 3000. Such olefin monomers are exemplified by ethylene, propylene,1-butene, 2-butene, isobutene, and mixtures thereof.

The preferred polyalkylene amines used to prepare the succinimides areof the formula:

wherein z is an integer of from 0 to 10 and Alk, R², R³, and R⁴ are asdefined above.

The alkylene amines include principally methylene amines, ethyleneamines, butylene amines, propylene amines, pentylene amines, hexyleneamines, heptylene amines, octylene amines, other polymethylene aminesand also the cyclic and the higher homologs of such amines as piperazineand amino alkyl-substituted piperazines. They are exemplifiedspecifically by ethylene diamine, triethylene tetraamine, propylenediamine, decamethyl diamine, octamethylene diamine, diheptamethylenetriamine, tripropylene tetraamine, tetraethylene pentamine, trimethylenediamine, pentaethylene hexamine, ditrimethylene triamine,2-heptyl-3-(2-aminopropyl)-imidazoline, 4-methyl imidazoline,N,N-dimethyl-1,3-propane diamine, 1,3-bis(2-aminoethyl)imidazoline,1-(2-aminopropyl)-piperazine, 1,4-bis(2-aminoethyl)piperazine and2-methyl-1-(2-aminobutyl)piperazine. Higher homologs such as areobtained by condensing two or more of the above-illustrated alkyleneamines likewise are useful.

The ethylene amines are especially useful. They are described in somedetail under the heading “Ethylene Amines” in Encyclopedia of ChemicalTechnology, Kirk-Othmer, Vol. 5, pp. 898-905 (Interscience Publishers,New York, 1950).

The term “ethylene amine” is used in a generic sense to denote a classof polyamines conforming for the most part to the structure

H₂N(CH₂CH₂NH)_(a)H

wherein a is an integer from 1 to 10.

Thus, it includes, for example, ethylene diamine, diethylene triamine,triethylene tetraamine, tetraethylene pentamine, pentaethylene hexamine,and the like.

Also included within the term “alkenyl succinimides” are post-treatedsuccinimides such as post-treatment processes involving ethylenecarbonate disclosed by Wollenberg, et al., U.S. Pat. No. 4,612,132;Wollenberg, et al., U.S. Pat. No. 4,746,446; and the like, as well asother post-treatment processes each of which are incorporated herein byreference in its entirety.

Preferably, the dispersant component, such as a polyalkylenesuccinimide, comprises from 2 to 40 weight percent, more preferably 5 to20 weight percent, and even more preferably 5 to 15 weight percent, ofthe weight of the oil dispersion of, hydrated alkali metal borate.

Polyalkylene succinic anhydrides or a non-nitrogen containing derivativeof the polyalkylene succinic anhydride (such as succinic acids, Group Iand/or Group II mono- or di-metal salts of succinic acids, succininateesters formed by the reaction of a polyalkylene succinic anhydride, acidchloride or other derivative with an alcohol, and the like) are alsosuitable dispersants for use in the compositions of this invention.

The polyalkylene succinic anhydride is preferably a polyisobutenylsuccinic anhydride. In one preferred embodiment, the polyalkylenesuccinic anhydride is a polyisobutenyl succinic anhydride having anumber average molecular weight of at least 500, more preferably atleast 900 to about 3000 and still more preferably from at least about900 to about 2300.

In another preferred embodiment, a mixture of polyalkylene succinicanhydrides is employed. In this embodiment, the mixture preferablycomprises a low molecular weight polyalkylene succinic anhydridecomponent and a high molecular weight polyalkylene succinic anhydridecomponent. More preferably, the low molecular weight component has anumber average molecular weight of from about 500 to below 1000 and thehigh molecular weight component has a number average molecular weight offrom 1000 to about 3000. Still more preferably, both the low and highmolecular weight components are polyisobutenyl succinic anhydrides.Alternatively, various molecular weights polyalkylene succinic anhydridecomponents can be combined as a dispersant as well as a mixture of theother above referenced dispersants as identified above.

As noted above, the polyalkylene succinic anhydride is the reactionproduct of a polyalkylene (preferably polyisobutene) with maleicanhydride. One can use conventional polyisobutene, or highmethylvinylidene polyisobutene in the preparation of such polyalkylenesuccinic anhydrides. One can use thermal, chlorination, free radical,acid catalyzed, or any other process in this preparation. Examples ofsuitable polyalkylene succinic anhydrides are thermal PIBSA(polyisobutenyl succinic anhydride) described in U.S. Pat. No.3,361,673; chlorination PIBSA described in U.S. Pat. No. 3,172,892; amixture of thermal and chlorination PIBSA described in U.S. Pat. No.3,912,764; high succinic ratio PIBSA described in U.S. Pat. No.4,234,435; PolyPIBSA described in U.S. Pat. Nos. 5,112,507 and5,175,225; high succinic ratio PolyPIBSA described in U.S. Pat. Nos.5,565,528 and 5,616,668; free radical PIBSA described in U.S. Pat. Nos.5,286,799, 5,319,030, and 5,625,004; PIBSA made from highmethylvinylidene polybutene described in U.S. Pat. Nos. 4,152,499,5,137,978, and 5,137,980; high succinic ratio PIBSA made from highmethylvinylidene polybutene described in European Patent ApplicationPublication No. EP 355 895; terpolymer PIBSA described in U.S. Pat. No.5,792,729; sulfonic acid PIBSA described in U.S. Pat. No. 5,777,025 andEuropean Patent Application Publication No. EP 542 380; and purifiedPIBSA described in U.S. Pat. No. 5,523,417 and European PatentApplication Publication No. EP 602 863. The disclosures of each of thesedocuments are incorporated herein by reference in their entirety.

Preferably, the polyalkylene succinic anhydride or other dispersantcomponent comprises from 2 to 40 weight percent, more preferably 5 to 20weight percent, and even more preferably 5 to 15 weight percent, of theweight of the oil dispersion of hydrated alkali metal borate.

Typically, in the oil dispersion of hydrated alkali metal borate, thehydrated alkali metal borate is in a ratio of at least 2:1 relative tothe polyalkylene succinic anhydride or other dispersant, whilepreferably being in the range of 2:1 to 10:1. In a more preferredembodiment the ratio is at least 5:1. In another preferred embodiment,mixtures as defined above of the polyalkylene succinic anhydrides areemployed.

The Detergent

The oil dispersion of hydrated alkali metal borate employed in theadditive compositions of the present invention may optionally contain adetergent. There are a number of materials that are suitable asdetergents for the purpose of this invention. These materials includephenates (high overbased or low overbased), high overbased phenatestearates, phenolates, salicylates, phosphonates, thiophosphonates andsulfonates and mixtures thereof. Preferably, sulfonates are used, suchas high overbased sulfonates, low overbased sulfonates, or phenoxysulfonates. In addition the sulfonic acids themselves can also be used.

The sulfonate detergent is preferably an alkali or alkaline earth metalsalt of a hydrocarbyl sulfonic acid having from 15 to 200 carbons.Preferably the term “sulfonate” encompasses the salts of sulfonic acidderived from petroleum products. Such acids are well known in the art.They can be obtained by treating petroleum products with sulfuric acidor sulfur trioxide. The acids thus obtained are known as petroleumsulfonic acids and the salts as petroleum sulfonates. Most of thepetroleum products which become sulfonated contain an oil-solubilizinghydrocarbon group. Also included within the meaning of “sulfonate” arethe salts of sulfonic acids of synthetic alkyl aryl compounds. Theseacids also are prepared by treating an alkyl aryl compound with sulfuricacid or sulfur trioxide. At least one alkyl substituent of the aryl ringis an oil-solubilizing group, as discussed above. The acids thusobtained are known as alkyl aryl sulfonic acids and the salts as alkylaryl sulfonates. The sulfonates where the alkyl is straight-chain arethe well-known linear alkylaryl sulfonates.

The acids obtained by sulfonation are converted to the metal salts byneutralizing with a basic reacting alkali or alkaline earth metalcompound to yield the Group I or Group II metal sulfonates. Generally,the acids are neutralized with an alkali metal base. Alkaline earthmetal salts are obtained from the alkali metal salt by metathesis.Alternatively, the sulfonic acids can be neutralized directly with analkaline earth metal base. The sulfonates can then be overbased,although, for purposes of this invention, overbasing is not necessary.Overbased materials and methods of preparing such materials are wellknown to those skilled in the art. See, for example, LeSuer U.S. Pat.No. 3,496,105, issued Feb. 17, 1970, particularly columns 3 and 4.

The sulfonates are present in the oil dispersion in the form of alkaliand/or alkaline earth metal salts, or mixtures thereof. The alkalimetals include lithium, sodium and potassium. The alkaline earth metalsinclude magnesium, calcium and barium, of which the latter two arepreferred.

Particularly preferred, however, because of their wide availability, aresalts of the petroleum sulfonic acids, particularly the petroleumsulfonic acids which are obtained by sulfonating various hydrocarbonfractions such as lubricating oil fractions and extracts rich inaromatics which are obtained by extracting a hydrocarbon oil with aselective solvent, which extracts may, if desired, be alkylated beforesulfonation by

reacting them with olefins or alkyl chlorides by means of an alkylationcatalyst; organic polysulfonic acids such as benzene disulfonic acidwhich may or may not be alkylated; and the like.

The preferred salts for use in the present invention are those ofalkylated aromatic sulfonic acids in which the alkyl radical or radicalscontain at least about 8 carbon atoms, for example from about 8 to 22carbon atoms. Another preferred group of sulfonate starting materialsare the aliphatic-substituted cyclic sulfonic acids in which thealiphatic substituents or substituents contain a total of at least 12carbon atoms, such as the alkyl aryl sulfonic acids, alkylcycloaliphatic sulfonic acids, the alkyl heterocyclic sulfonic acids andaliphatic sulfonic acids in which the aliphatic radical or radicalscontain a total of at least 12 carbon atoms. Specific examples of theseoil-soluble sulfonic acids include petroleum sulfonic acids, mono- andpoly-wax-substituted naphthalene sulfonic acids, substituted sulfonicacids, such as cetyl benzene sulfonic acids, cetyl phenyl sulfonicacids, and the like, aliphatic sulfonic acid, such as paraffin waxsulfonic acids, hydroxy-substituted paraffin wax sulfonic acids, etc.,cycloaliphatic sulfonic acids, petroleum naphthalene sulfonic acids,cetyl cyclopentyl sulfonic acid, mono- and poly-wax-substitutedcyclohexyl sulfonic acids, and the like. The term “petroleum sulfonicacids” is intended to cover all sulfonic acids that are derived directlyfrom petroleum products.

Typical Group II metal sulfonates suitable for use in the presentinvention include the metal sulfonates exemplified as follows: calciumwhite oil benzene sulfonate, barium white oil benzene sulfonate,magnesium white oil benzene sulfonate, calcium dipolypropene benzenesulfonate, barium dipolypropene benzene sulfonate, magnesiumdipolypropene benzene sulfonate, calcium mahogany petroleum sulfonate,barium mahogany petroleum sulfonate, magnesium mahogany petroleumsulfonate, calcium triacontyl sulfonate, magnesium triacontyl sulfonate,calcium lauryl sulfonate, barium lauryl sulfonate, magnesium laurylsulfonate, etc. The concentration of metal sulfonate that may beemployed may vary over a wide range, depending upon the concentration ofalkali metal borate particles. When present, however, the detergentconcentration will generally range from about 0.2 to about 10 weightpercent and preferably from about 3 to about 7 weight percent, based onthe total weight of the oil dispersion of the hydrated borate. Inaddition, the compositions of this invention may contain a mixture ofboth a metal sulfonate and an ashless dispersant, as described above,where the ratio is a factor of achieving the proper stability of the oildispersion of the hydrated alkali metal borate.

The Oil of Lubricating Viscosity

The lubricating oil to which the hydrated alkali metal borate and thedispersant are added to form the oil dispersion of the hydrated alkalimetal borate can be any hydrocarbon-based lubricating oil or a syntheticbase oil stock. Likewise, these lubricating oils can be added to the oildispersion of hydrated alkali metal borate and additive compositionscontaining them, as described herein, in additional amounts, to formfinished oil compositions. The hydrocarbon-based lubricating oils may bederived from synthetic or natural sources and may be paraffinic,naphthenic or aromatic base, or mixtures thereof. The diluent oil can benatural or synthetic, and can be different viscosity grades.

In the oil dispersion of the hydrated alkali metal borate, thelubricating oil typically comprises from about 30 to 70 weight percent,more preferably from about 45 to 55 weight percent, based on the totalweight of the oil dispersion of the hydrated alkali metal borate.

In general the oil dispersion of hydrated alkali metal borate is presentin the additive composition of the invention in the range of about 10 to90 weight percent, based on the total weight of the additivecomposition.

The Oil Dispersion of Hexagonal Boron Nitride

The additive composition of the present invention further contains anoil dispersion of hexagonal boron nitride.

Hexagonal boron nitride, or h-BN, is a hexagonal, graphite-like form ofboron nitride, having a layered structure and planar 6-membered rings ofalternating boron and nitrogen atoms. On alternate sheets, boron atomsare directly over nitrogen atoms. Hexagonal boron nitride can beprepared by heating boric oxide, boric acid or boric acid salts withammonium chloride, alkali cyanides or calcium cyanamide at atmosphericpressure. Hexagonal boron nitride may also be prepared by the reactionof boron trichloride or boron trifluoride with ammonia. A discussion ofhexagonal boron nitride can be found, for example, in Kirk-Othmer,Encyclopedia of Chemical Technology, Fourth Edition, Vol. 4, pp.427-429, John Wiley and Sons, New York, 1992.

Generally, the hexagonal boron nitride will have a mean particle size ofless than 1 micron. Preferably, the hexagonal boron nitride will have aparticle size distribution wherein 90% or greater of the particles areless than about 0.5 microns (500 nanometers, m), with a preferred meanparticle size of less than about 0.3 microns (300 nm).

Typically, the oil dispersion of the hexagonal boron nitride willcontain about 1 to about 50 weight percent of the hexagonal boronnitride, preferably about 1 to about 20 weight percent, and morepreferably about 5 to about 15 weight percent, based on the total weightof the oil dispersion.

Preferably, the oil dispersion of the hexagonal boron nitride willcontain a surfactant as a stabilizer for the oil dispersion. Typicalsurfactants for use as a stabilizer include ethylene-propylenecopolymers, or terpolymers of ethylene, propylene and an unconjugateddiene commonly known as ethylene-propylene-diene terpolymer,ethylene-propylene copolymers grafted with a nitrogen-containing vinylfunctionality selected from the group consisting of N-vinyl pyrrollidoneand N-vinyl pyridine, and the like. The ethylene-propylene copolymergenerally has an average molecular weight in the range of about 22,000to 200,000. A preferred surfactant is ethylene-propylene copolymer whichhas substantially equal proportions of ethylene and propylene monomersand an average molecular weight of from 22,000 to about 40,000. Whenpresent, the surfactant concentration in the oil dispersion of hexagonalboron nitride will typically range from about 0.1 to about 25 weightpercent, preferably from about 2 to about 7 weight percent, and morepreferably from about 3.0 to about 5.0 weight percent, based on thetotal weight of the oil dispersion of hexagonal boron nitride.

The lubricant oil used to prepare the oil dispersion of the hexagonalboron nitride may be selected from the same group of natural orsynthetic lubricating oils described above for use in preparing the oildispersion of the hydrated alkali metal borate, but other carrier fluidshave been found to be satisfactory, including vegetable oils such asrapeseed oil; liquid hydrocarbons such as aliphatic and aromaticnaphthas and mixtures thereof; synthetic lubricant fluids such aspolyalphaolefins, polyglycols, diester fluids, and mixtures of theseliquids. Moreover, the oil used in forming the oil dispersion ofhexagonal boron nitride may be the same as, or different from, thelubricant oil employed in preparing the oil dispersion of hydratedalkali metal borate. Typical oils for preparing the oil dispersion ofhexagonal boron nitride include the Group I and Group II base oils, suchas 150 solvent neutral petroleum oil.

In general, the oil dispersion of hexagonal boron nitride is present inthe additive composition of the invention in the range of about 10 to 90weight percent, based on the total amount of the additive composition.

Formulations

The additive compositions of the present invention containing oildispersions of alkali metal borate and hexagonal boron nitride (asdescribed hereinabove) may be blended further with additional additivesto form additive packages containing the present additive compositions.These additive packages typically comprise from about 10 to 80 weightpercent of the additive composition of the present invention describedabove and from about 90 to 20 weight percent of one or more ofconventional additives selected from the group consisting of ashlessdispersants (0-10%), detergents (0-5%), sulfurized hydrocarbons (0-40%),dialkyl hydrogen phosphates (0-15%), zinc dithiophosphates (0-20%),alkyl ammonium phosphates and/or thio-dithiophosphates (0-20%),phosphites (0 to 10%) fatty acid esters of polyalcohols (0-10%),2,5-dimercaptothiadiazole (0-5%), benzotriazole (0-5%), dispersedmolybdenum disulfide (0-5%), foam inhibitors (0-2%), and imidazolines(0-10%) and the like, wherein each weight percent is based on the totalweight of the composition.

Fully formulated finished oil compositions of this invention can beformulated from these additive packages upon further blending with anoil of lubricating viscosity. Preferably, the additive package describedabove is added to an oil of lubricating viscosity in an amount of fromabout 1 to 20 weight percent, preferably about 2 to 15 weight percent,to provide for the finished oil composition wherein the weight percentof the additive package is based on the total weight of the composition.

A variety of other additives can be present in lubricating oils of thepresent invention. These additives include antioxidants, rustinhibitors, corrosion inhibitors, extreme pressure agents, antifoamagents, other anti-wear agents, and a variety of other well-knownadditives in the art.

EXAMPLES

The invention will be further illustrated by the following examples,which set forth particularly advantageous embodiments. While theexamples are provided to illustrate the present invention, they are notintended to limit it.

Example 1

The additive composition of the present invention was evaluated in alubricating oil for its anti-sticking properties following a test usingan SAE No. 2 bench, which evaluates transmission fluids duringsynchronization. The friction pairs used in this bench comprised a brasssynchronizer ring and a steel gear cone.

During each cycle of the test, the cone is rotating, at a given speed,then the ring moves along the axis of the cone for its braking until itis blocked. At the end of each cycle, the ring is disengaged.

If sticking occurs, a sticking torque is measured when rotation of thecone is resumed. During the test, the lubricating oil and the metalparts are heated to a temperature between about 60° C. and 90° C. Thecontact pressure is about 20 MPa and the initial sliding speed is 1.6m/s.

The anti-sticking coefficient for this test was calculated as follows:

${{Anti}\text{-}{sticking}\mspace{14mu} {coefficient}} = {1 - \frac{\left( {{{No}.\mspace{14mu} {of}}\mspace{14mu} {cycles}\mspace{14mu} {with}\mspace{14mu} {sticking}} \right)}{\left( {{Total}\mspace{14mu} {{No}.\mspace{14mu} {of}}\mspace{14mu} {cycles}\mspace{14mu} {in}\mspace{14mu} {test}} \right)}}$

Accordingly, an anti-sticking coefficient of 0 indicates the presence ofcone on ring sticking during every cycle of the test. Conversely, ananti-sticking coefficient of 1 indicates no sticking at all was observedover the entire duration of the test. Thus, the higher the anti-stickingcoefficient, up to a maximum of 1, the better the anti-stickingperformance of the lubricating oil.

The test lubricating oil compositions were formulated as follows.

Lubricant Composition 1

A lubricant composition was prepared containing the following:

-   -   (a) 7 weight percent of an oil dispersion of hydrated potassium        triborate, wherein the oil dispersion contained about 30 weight        percent of the hydrated potassium triborate, dispersed in a 150        N neutral oil;    -   (b) 10 weight percent of an oil dispersion of hexagonal boron        nitride, wherein the oil dispersion contained about 10 weight        percent of the hexagon boron nitride solids, dispersed in a 150        N neutral oil containing a stabilizing agent; and    -   (c) 83 weight percent of a 50/50 mixture of neutral oil (150N        plus 600N) and a synthetic polyalphaolefin oil.

Lubricant Composition 2

The lubricant composition 2 was prepared containing the following:

-   (a) 7 weight percent of an oil dispersion of hydrated potassium    triborate, wherein the oil dispersion contained about 30 weight    percent of the hydrated potassium triborate, dispersed in a 150 N    neutral oil;-   (b) 5 weight percent of an oil dispersion of hexagonal boron    nitride, wherein the oil dispersion contained about 10 weight    percent of the hexagon boron nitride solids, dispersed in a 150 N    neutral oil containing a stabilizing agent; and-   (c) 88 weight percent of a 50/50 mixture of neutral oil (150N plus    600N) and a synthetic polyalphaolefin oil.

Lubricant Composition 3

The lubricant composition 3 was prepared containing the following:

-   (a) 7 weight percent of an oil dispersion of hydrated potassium    triborate, wherein the oil dispersion contained about 30 weight    percent of the hydrated potassium triborate, dispersed in a 150 N    neutral oil;-   (b) 2.5 weight percent of an oil dispersion of hexagonal boron    nitride, wherein the oil dispersion contained about 10 weight    percent of the hexagon boron nitride solids, dispersed in a 150 N    neutral oil containing a stabilizing agent; and-   (c) 90.5 weight percent of a 50/50 mixture of neutral oil (150N plus    600N) and a synthetic polyalphaolefin oil.

Lubricant Composition A (Comparative)

A lubricating composition was prepared containing the following:

-   -   (a) 7 weight percent of an oil dispersion of hydrated potassium        triborate, wherein the oil dispersion contained about 30 weight        percent of the hydrated potassium triborate, dispersed in a 150        N neutral oil; and    -   (b) 93 weight percent of a 50/50 mixture of neutral oil (150N        plus 600N) and a synthetic polyalphaolefin oil.

Lubricant Composition B (Comparative)

A lubricating composition was prepared containing the following:

-   -   (a) 10 weight percent of an oil dispersion of hexagonal boron        nitride, wherein the oil dispersion contains about 10 weight        percent of the hexagonal boron nitride solids, dispersed in a        150 N neutral oil containing a stabilizing agent; and    -   (b) 90 weight percent of a 50/50 mixture of neutral oil (150N        plus 600N) and a synthetic polyalphaolefin oil.

The above lubricant compositions were evaluated for anti-stickingperformance in the synchronization test described above. A base oilcontaining a 50/50 mixture of 150N and 600N neutral oil, with noadditives, was also tested. The results of this evaluation are shown inTable 1:

TABLE 1 No. of Cycles with Cone Total No. of Anti-sticking Sample onRing Sticking Cycles coefficient Base oil 5000 5000 0 Comparative 81008100 0 Composition A Comparative 6600 6600 0 Composition B Composition 11200 7500 0.84 Composition 2 1600 8710 0.82 Composition 3 300 10560 0.97

The above data demonstrates that the additive composition of the presentinvention provides significant anti-sticking performance and shows amarked improvement over the comparative compositions.

From the foregoing description, various modifications and changes in theabove-described invention will occur to those skilled in the art. Allsuch modifications coming within the scope of the appended claims areintended to be included therein.

1. An additive composition for a transmission oil comprising: (a) an oildispersion of a hydrated potassium borate; and (b) an oil dispersion ofhexagon boron nitride; wherein the weight ratio of the hydratedpotassium borate to the hexagonal boron nitride is in the range of about2.1:1.0 to about 8.4:1.0.
 2. The additive composition according to claim1, wherein the hydrated potassium borate is hydrated potassiumtriborate.
 3. The additive composition according to claim 1, wherein theoil dispersion of hydrated potassium borate contains a hydratedpotassium borate, a dispersant and an oil of lubricating viscosity. 4.The additive composition according to claim 3, wherein the oildispersion of hydrated potassium borate contains about 10 to about 75weight percent of the hydrated potassium borate, based on the totalweight of the oil dispersion.
 5. The additive composition according toclaim 3, wherein the oil dispersion of hydrated potassium boratecontains about 2 to about 40 weight percent of the dispersant, based onthe total weight of the oil dispersion.
 6. The additive compositionaccording to claim 3, wherein the oil dispersion of hydrated potassiumborate further contains a detergent.
 7. The additive compositionaccording to claim 6, wherein the oil dispersion of hydrated potassiumborate contains about 0.2 to about 10 weight percent of the detergent,based on the total weight of the oil dispersion.
 8. The additivecomposition according to claim 1, wherein the oil dispersion of hydratedpotassium borate is present in the additive composition in the range ofabout 10 to about 90 weight percent, based on the total weight of theadditive composition.
 9. The additive composition according to claim 1,wherein the hexagonal boron nitride has a particle size distributionwherein 90% or greater of the particles are less than about 0.5 microns.10. The additive composition according to claim 1, wherein the oildispersion of hexagonal boron nitride contains an oil of lubricatingviscosity and about 1 to about 50 weight percent of hexagonal boronnitride, based on the total weight of the oil dispersion.
 11. Theadditive composition according to claim 12, wherein the oil dispersionof hexagonal boron nitride further contains a surfactant as astabilizer.
 12. The additive composition according to claim 1, whereinthe oil dispersion of hexagonal boron nitride is present in the additivecomposition in the range of about 10 to about 90 weight percent, basedon the total weight of the additive composition.
 13. A lubricating oilcomposition comprising a major amount of a transmission oil oflubricating viscosity and an effective synchronizer sticking reducingamount of an additive composition comprising: (a) an oil dispersion on ahydrated potassium borate; and (b) an oil dispersion of hexagonal boronnitride; wherein the weight ratio of the hydrated potassium borate tothe hexagonal boron nitride is in the range of about 2.1:1.0 to about8.4:1.0.
 14. The lubricating oil composition according to claim 13,wherein the transmission oil is a manual transmission gear oil.